Effects of Cross and Self Fertilisation in the Vegetable Kingdom eBook

Fertility of plants of crossed and self-fertilised
parentage, both lots being fertilised in the same
manner. Fertility of the parent-plants when first
crossed and self-fertilised, and of their crossed
and self-fertilised offspring when again crossed and
self-fertilised. Comparison of the fertility
of flowers fertilised with their own pollen and with
that from other flowers on the same plant. Self-sterile
plants. Causes of self-sterility. The appearance
of highly self-fertile varieties. Self-fertilisation
apparently in some respects beneficial, independently
of the assured production of seeds. Relative
weights and rates of germination of seeds from crossed
and self-fertilised flowers.

The present chapter is devoted to the Fertility of
plants, as influenced by cross-fertilisation and self-fertilisation.
The subject consists of two distinct branches; firstly,
the relative productiveness or fertility of flowers
crossed with pollen from a distinct plant and with
their own pollen, as shown by the proportional number
of capsules which they produce, together with the
number of the contained seeds. Secondly, the
degree of innate fertility or sterility of the seedlings
raised from crossed and self-fertilised seeds; such
seedlings being of the same age, grown under the same
conditions, and fertilised in the same manner.
These two branches of the subject correspond with the
two which have to be considered by any one treating
of hybrid plants; namely, in the first place the comparative
productiveness of a species when fertilised with pollen
from a distinct species and with its own pollen; and
in the second place, the fertility of its hybrid offspring.
These two classes of cases do not always run parallel;
thus some plants, as Gartner has shown, can be crossed
with great ease, but yield excessively sterile hybrids;
while others are crossed with extreme difficulty, but
yield fairly fertile hybrids.

The natural order to follow in this chapter would
have been first to consider the effects on the fertility
of the parent-plants of crossing them, and of fertilising
them with their own pollen; but as we have discussed
in the two last chapters the relative height, weight,
and constitutional vigour of crossed and self-fertilised
plants—­that is, of plants raised from crossed
and self-fertilised seeds—­it will be convenient
here first to consider their relative fertility.
The cases observed by me are given in Table 9/D, in
which plants of crossed and self-fertilised parentage
were left to fertilise themselves, being either crossed
by insects or spontaneously self-fertilised. It
should be observed that the results cannot be considered
as fully trustworthy, for the fertility of a plant
is a most variable element, depending on its age,
health, nature of the soil, amount of water given,
and temperature to which it is exposed. The number
of the capsules produced and the number of the contained
seeds, ought to have been ascertained on a large number